Discrimination medium and production method therefor

ABSTRACT

A discrimination medium, which can have much information, can be produced on a small scale at low cost, and enables change of a sticker design at low cost, is provided. A cholesteric liquid crystal layer, having a fine asperity for forming a hologram, is formed on a transparent first substrate. A print layer composed of a black ink is formed on a transparent second substrate. The substrates are affixed to each other via a bond layer, so that a discrimination medium is obtained. In the discrimination medium, the display content obtained by the print layer is changed, so that the display content for discrimination can be changed at low cost.

TECHNICAL FIELD

The present invention relates to a discrimination medium for determiningwhether or not various products are authentic. In particular, thepresent invention relates to a discrimination medium which can have muchinformation, can be redesigned at low cost, and is suitable for smallscale production. The present invention relates to a production methodfor the discrimination medium.

BACKGROUND ART

In order to prevent counterfeiting of passports, various cards,certificates, various products, and the like, techniques of coating aspecial ink on a surface of an article have been known, and techniquesof applying a hologram on a surface of an article have been known. Forexample, Japanese Unexamined Patent Application Publication No. Hei11-042875 has disclosed an anticounterfeiting technique using acholesteric liquid crystal with a hologram. In this technique, acholesteric liquid crystal and a hologram are combined, and a reflectionlight therefrom is observed via a left circular polarization filter anda right circular polarization filter, so that the authenticity can bedetermined. Specifically, when the hologram can be observed via theright circular polarization filter, the hologram cannot be observed viathe left circular polarization filter. The authenticity of the articlecan be determined by using this phenomenon.

However, in the above technique, since only the hologram can haveinformation (logo, production lot, and the like), the information amountmay be a little. Since a block used for hologram production isexpensive, the technique may not be suitable for small-scale production,and change of figure may require high cost.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a discrimination mediumwhich can have much information, can be produced on a small scale at lowcost, and can be redesigned at low cost. Another object of the presentinvention is to provide a production method therefor.

According to one aspect of the present invention, a discriminationmedium includes: a cholesteric liquid crystal layer which has a fineasperity used for displaying a hologram; and a print layer which has apredetermined pattern reflecting or absorbing a light of a predeterminedwavelength, wherein the cholesteric liquid crystal layer and the printlayer are disposed in turn from a side checked visually.

In the above aspect of the present invention, various information can bedisplayed by combination of displays of the hologram and the printpattern of the print layer. The display content used for discriminationcan be changed at low cost by changing the print pattern of the printlayer which can be produced at low cost. In the one aspect of thepresent invention, another layer may be provided between the cholestericliquid crystal layer and the print layer. The cholesteric liquid crystallayer and the print layer may contact each other. The contents ofdisplays of the hologram and the print pattern of the print layer caninclude characters, designed characters, figures, patterns, orcombination of at least two selected from them.

According to a desirable embodiment of the present invention, thediscrimination medium further may include: a first substrate which isoptically transparent and on which the cholesteric liquid crystal layeris formed; and a second substrate which is optically transparent and onwhich the print layer is formed, wherein the first substrate and thesecond substrate are affixed to each other. The optical transparency ofmaterial may be a property in which the material allows visible light topass therethrough. It may be desirable that visible light transmittanceratio be higher, and an optical loss, which is within a range which doesnot affect discrimination using the discrimination medium, may begenerated.

In the above embodiment of the present invention, the display contentfor discrimination can be changed by changing the pattern of the printlayer of the second substrate side. The change of the pattern of theprint layer can be performed at low cost, so that the cost for thechange of the display content can be reduced.

According to a desirable embodiment of the present invention, the printlayer may be provided on a surface of the cholesteric liquid crystallayer on which the fine asperity is formed. In this embodiment of thepresent invention, the print layer, which is formed on the cholestericliquid crystal layer, is changed without changing of the cholestericliquid crystal layer, so that the display content for discrimination canbe changed. The change of the print layer can be performed at low cost,so that the cost for acquisition of different display content can bereduced.

According to another aspect of the present invention, a productionmethod for a discrimination medium includes steps of: forming acholesteric liquid crystal layer on a first substrate which is opticallytransparent; forming a fine asperity on a surface of the cholestericliquid crystal layer, the fine asperity used for displaying a hologram;forming a print layer on a second substrate which is opticallytransparent, the print layer having a predetermined pattern reflectingor absorbing a light of a predetermined wavelength; and affixing thefirst substrate and the second substrate to each other.

In the above aspect of the present invention, display content of thediscrimination medium can be changed by changing the second substrateside. The change of the pattern of the print layer can be performed atlow cost, so that the cost for the change of the second substrate sidecan be reduced. Thus, plural variations are prepared for the secondsubstrate side, so that the discrimination medium, which can displayvarious contents, can be produced without increasing cost. Thepredetermined wavelength may be a specific wavelength of 700 nm or aband of wavelength having a width (for example, a band of wavelength ofoverall range of visible light.

According to another aspect of the present invention, a productionmethod for a discrimination medium includes steps of: forming acholesteric liquid crystal layer on a first substrate which is opticallytransparent; forming a fine asperity on a surface of the cholestericliquid crystal layer, the fine asperity used for displaying a hologram;and forming a print layer on the surface of the cholesteric liquidcrystal layer on which the fine asperity is formed, the print layerhaving a predetermined pattern reflecting or absorbing a light of apredetermined wavelength. In this aspect of the present invention,display content for discrimination can be changed by only changing theprocess for forming the print layer.

According to the present invention, a discrimination medium, which canhave much information, can be produced on a small scale at low cost, andcan be redesigned at low cost, can be provided, and a production methodfor the discrimination medium can provided.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a conceptual diagram for explaining a structure of cholestericliquid crystal.

FIG. 2 is a conceptual diagram for explaining optical characteristics ofcholesteric liquid crystal.

FIGS. 3A to 3E are diagrams showing one example of production processesfor discrimination medium using one embodiment of the present invention.

FIGS. 4A to 4C are diagrams showing one example of a discriminationfunction of a discrimination medium using one embodiment of the presentinvention.

FIGS. 5A to 5C are diagrams showing one example of a discriminationfunction of a discrimination medium using one embodiment of the presentinvention.

FIGS. 6A to 6E are diagrams showing another example of productionprocesses for a discrimination medium using one embodiment of thepresent invention.

EXPLANATION OF REFERENCE NUMERALS

301 denotes a transparent first substrate, 302 denotes a cholestericliquid crystal layer, 303 denotes a fine asperity processed portion forhologram display, 304 denotes a transparent second substrate, 305denotes a print layer, 306 denotes an adhesive layer, 307 denotes arelease sheet, 308 denotes a transparent bond layer, 310 denotes adiscrimination medium, 31 denotes a first substrate side member, and 32denotes a second substrate side member.

BEST MODE FOR CARRYING OUT THE INVENTION 1. First Embodiment RegardingCholesteric Liquid Crystal

First, cholesteric liquid crystal will be simply explained. FIG. 1 is aconceptual diagram for explaining a structure of cholesteric liquidcrystal. FIG. 2 is a conceptual diagram for explaining opticalcharacteristics of cholesteric liquid crystal. As shown in FIG. 2, whennatural light enters to a cholesteric liquid crystal layer 201, aright-handed circularly polarized light having a predeterminedwavelength is reflected by the cholesteric liquid crystal layer 201. Aleft-handed circularly polarized light, a linearly polarized light, anda right-handed circularly polarized light having another predeterminedwavelength pass through the cholesteric liquid crystal layer 201.

The cholesteric liquid crystal layer has a stacked structure. In onelayer, long axes of liquid crystal molecules have the same orientationand are parallel to the plane thereof in a surface of a layer. Layers ofthe stacked structure, which are adjacent to each other, are slightlydifferent from each other in a direction of the orientation, and thelayers are stacked with the orientations rotating in a three-dimensionalspiral structure overall.

In this structure, in a direction perpendicular to the layer, pitch P isa distance necessary for the molecular long axis to be rotated through360° and return to the initial state, and an average refraction index ofthe each layer is index n. In this case, the cholesteric liquid crystallayer selectively reflects circularly polarized light having a centerwavelength λs satisfying the equation λs=n×P. That is, when white lightenters to the cholesteric liquid crystal layer, a right-handed orleft-handed circularly polarized light having a predetermined centerwavelength is selectively reflected. In this case, circularly polarizedlight, which has the same circling direction as the reflected circularlypolarized light but does not have the wavelength of λs, passes throughthe cholesteric liquid crystal layer, a circularly polarized light,which has a circling direction reverse to the reflected circularlypolarized light, passes through the cholesteric liquid crystal layer,and a linearly polarized light passes through the cholesteric liquidcrystal layer.

The circling direction (rotating direction) of the reflected circularlypolarized light is determined by selecting a spiral direction of thecholesteric liquid crystal layer. That is, when the long axes are seenfrom the incident direction of the light, by selecting either the spiraldirection in which the molecular long axis of each layer orientation isclockwise or counterclockwise, the circling direction (rotatingdirection) of the reflected circularly polarized light can bedetermined.

The cholesteric liquid crystal layer exhibits color shift phenomenon.The principle of the color shift will be explained hereinafter. When alight obliquely enters to a multilayer film having a multilayerstructure, the light reflects at each interface of the multilayerstructure. In this case, the layers, which are adjacent to each otherand are optically transparent, have refraction indexes different fromeach other. These reflections are caused by the difference of therefractive indexes of the transparent films adjacent to each other. Whenone interface is viewed, the incident light is partially reflected andmost of it is transmitted. That is, the light entering to the interfacesof the laminated films is reflected at each interface little by little.The light is basically reflected in the same direction at eachinterface, so that interference occurs depending on optical pathdifferences.

When the incident light enters to the films from a directionapproximately parallel to the surface, the optical path difference issmall, and the light of shorter wavelengths interferes and isreinforced. In this way, when the viewing angle is increased, thereflected light of the shorter wavelengths interferes and is reinforced.As a result, when the multilayer film is viewed under white light, itappears to have a predetermined color at a viewing angle of 0 degree. Incontrast, as the viewing angle is increased, the multilayer filmgradually changes color to a bluish state. The phenomenon observed inthis manner is called the color shift phenomenon. The viewing angle isan angle between a line of vision and a line perpendicular to the layer.

Production Method for Discrimination Medium and Structure ofDiscrimination Medium

First, one example of production processes for discrimination mediumusing one embodiment of the present invention will be explained. FIGS.3A to 3E are cross sectional views showing one example of productionprocesses for discrimination medium using one embodiment of the presentinvention. First, a first substrate 301, which is optically transparentand functions as a surface protection layer, is prepared (in FIG. 3A).In this case, the transparent first substrate 301 may be film-like onewhich is composed of TAC (triacetyl cellulose) and has a thickness of 40μm. The first substrate 301 has an isotropic refraction index in orderto maintain the circular polarization condition of the light passingthrough the first substrate 301. For example, a polycarbonate and apolystyrene can be used as a material of the first substrate 301 whichsatisfies the above condition.

After the first substrate 301 is prepared, for example, a cholestericliquid crystal layer 302 having a thickness of 2 μm is formed on thefirst substrate 301. Thus, the condition shown in FIG. 3A is obtained. Alayer, which exhibits optically selective reflection property andcircular polarization selectivity, can be used as the cholesteric liquidcrystal layer 302. In particular, a polymer film of which cholestericliquid crystal orientation is fixed is desirably used. A film, in whichcholesteric liquid crystal grains are dispersed in supports, or the likemay be used.

One example of the polymer film, of which cholesteric liquid crystalorientation is fixed, is produced as follows. For example, a lowmolecular liquid crystal is oriented in a cholesteric orientation. Then,the low molecular liquid crystals are joined by photoreaction, thermalreaction, or the like, and the molecular orientation is fixed. As aresult, a polymer film, of which cholesteric liquid crystal orientationis fixed, can be produced. Alternatively, a thermotropic polymer liquidcrystal of the branched-chain type or the straight-chain type may beoriented in a cholesteric orientation in a liquid crystal condition.Then, the cholesteric liquid crystal orientation thereof is fixed bycooling to a temperature of the liquid crystal transition point orlower. As a result, a polymer film, of which cholesteric liquid crystalorientation is fixed, can be produced. Alternatively, a lyotropicpolymer liquid crystal of the branched-chain type or the straight-chaintype may be oriented in a cholesteric orientation in a solvent, and themolecular orientation thereof is fixed by gradually removing thesolvent. As a result, a polymer film, of which cholesteric liquidcrystal orientation is fixed, can be produced.

As a polymer liquid crystal for production of the above polymer films, abranched-chain type polymer having a liquid crystal forming group in abranched-chain, such as a polyacrylate, a polymethacrylate, apolysiloxane, and a polymalonate may be used. Alternatively, astraight-chain type polymer having a liquid crystal forming group in astraight chain, such as a polyester, a polyester amide, a polycarbonate,a polyamide, and a polyimide may be used.

After the condition shown in FIG. 3A is obtained, the cholesteric liquidcrystal layer 302 is pressed on a block (mold), which is used forforming a hologram, on the cholesteric liquid crystal layer 302, so thata fine asperity (emboss) 303, which has recesses and projections andforms an hologram image, is formed (in FIG. 3B). Thus, a first substrateside member 31 is obtained. As shown in FIG. 3B, the first substrateside member 31 has a stacked structure having the first substrate 301and the cholesteric liquid crystal layer 302 provided on a surfacethereof. In this case, the first substrate 301 is used as a base member,and the cholesteric liquid crystal layer 302 has the fine asperity whichforms the hologram image.

A member shown in FIG. 3C, which is different from the above firstsubstrate side member 31, is produced. This member is a second substrateside member 32 has a second substrate 304, a print layer 305, and anadhesive layer 306. The second substrate 304 is a plastic substratewhich is optically transparent. For example, the second substrate 304 isa substrate which is composed of PET (polyethylene terephthalate) andhas a thickness of 15 μm. The print layer 305 has a pattern which formsa predetermined figure printed on a surface of the second substrate 304.The print layer 305 is provided by printing a black ink on the surfaceof the second substrate 304. The adhesive layer 306 covers the printlayer 305. The adhesive layer 306 is used for affixing a discriminationmedium onto an article which is discriminated by the discriminationmedium. The adhesive layer 306 is composed of a resin type adhesivehaving stable adhesion. The adhesive layer 306 may has lightpermeability, light absorptivity, or light reflectivity. When theadhesive layer 306 may has light reflectivity or light absorptivity, itis necessary that the adhesive layer 306 exhibit a color different fromthe print layer 305 and have an appearance different from the printlayer 305. In the example shown in FIG. 3C, release sheet 307 is affixedto a surface on which the adhesive layer 306 is exposed.

As described above, the first substrate side member 31 shown in FIG. 3Band the second substrate side member 32 shown in FIG. 3C are obtained.Next, the surface and the reverse surface of the second substrate sidemember 32 are reversed, and a second substrate side member 32′ is set(in FIG. 3D). A bond or an adhesive, which is optically transparent, iscoated on the surface adjacent to the second substrate 304, so that atransparent bond layer 308 is formed. The bond or the adhesive of thebond layer 308 may be transparent resin type one which is commerciallyavailable. Regarding the bond, the material of the bond may be cured andmay thereby exert a bonding force. Regarding the adhesive, the adhesionforce of the adhesive may not be lost and be maintained.

On the other hand, the surface and the reverse surface of the firstsubstrate side member 31 are reversed, and a first substrate side member31′ is set (in FIG. 3D). The surface of the fine asperity 303 forhologram display of the cholesteric liquid crystal layer 302 is faced tothe bond layer 308 of the second substrate side member 32′. Thus, thecondition shown in FIG. 3D is obtained. Next, the bond layer 308 iscontacted on the cholesteric liquid crystal layer 302, and the firstsubstrate 301 and the second substrate 304 are bonded to each other. Asa result, a discrimination medium 310 shown in FIG. 3E is obtained.

The discrimination medium 310 shown in FIG. 3E has a stacked structuresuch that the transparent first substrate 301, the cholesteric liquidcrystal layer 302, the transparent bond layer 308, the transparentsecond substrate 304, the black print layer 305, the adhesive layer 306are stacked in turn from a side checked visually in observing thediscrimination medium 310. The first substrate 301 functions as aprotection layer. The cholesteric liquid crystal layer 302 has thehologram formed on the surface thereof. The print layer 305 has thepredetermined pattern. In order to secure the discrimination medium 310onto an article, the release sheet 307 is peeled, the adhesive layer 306is contacted on a surface of the article, and the discrimination medium310 is affixed to the article by the adhesion force of the adhesivelayer 306. In FIG. 3E, from a side checked visually in observing thediscrimination medium 310, the second substrate 304 and the print layer305 are disposed in turn. Alternatively, the print layer 305 and thesecond substrate 304 may be disposed in turn.

Example 1 of Discrimination Function of Embodiment

FIGS. 4A to 4C are conceptual diagrams showing an outline of adiscrimination function of the discrimination medium 310 shown in FIG.3E. In this example, the cholesteric liquid crystal layer 302 shown inFIG. 3E is set to selectively reflect a right-handed circularlypolarized green light. Characters “ABCDEFG . . . ” are displayed as ahologram display by the fine asperity 303 used for hologram display.Patterns of “▴” and “●” are displayed by a print pattern of the blackprint layer 305. In the example shown in FIGS. 4A to 4C, the adhesivelayer 306 shown in FIG. 3E is transparent, and a surface of the articleon which discrimination medium 310 is affixed, is whitish.

FIG. 4A shows a condition in which the discrimination medium 310 isobserved from a side of the first substrate 301 by a direct visualcheck. In this case, a reflection light from the cholesteric liquidcrystal layer 302 is visually confirmed, and a reflection light from thelayers under the cholesteric liquid crystal layer 302 is visuallyconfirmed. That is, since the reflection light from the cholestericliquid crystal layer 302 can be observed, the hologram display (thecharacters “ABCDEFG . . . ”), which are formed on the cholesteric liquidcrystal layer 302, can be observed. A portion of components of light,which passed through the cholesteric liquid crystal layer 302, isabsorbed by the black print layer 305. Another component of the lightpasses through the transparent adhesive layer 306, and is reflected bythe whitish surface of the article, and it exits through the oppositepassage from the discrimination medium 310. Thus, in addition to thecharacters “ABCDEFG . . . ”, blackish displays of the patterns of “▴”and “●” can be visually observed. Since there is a reflection light fromthe cholesteric liquid crystal layer 302 which is above the print layer305, a portion of the characters “ABCDEFG . . . ” can be observed in theblackish displays of the patterns of “▴” and “●”.

When the viewing angle is changed in the condition shown in FIG. 4A,color shift phenomenon occurs, and the color of the discriminationmedium 310 shifts toward the color of shorter wavelengths. In this case,the portions “▴” and “●” are formed on the black print layer absorbingvisible light, reflection light from the cholesteric liquid crystallayer 302 is relatively visible at these portions. Thus, the color shiftphenomenon can be clearly observed.

When an optical filter, which allows a right-handed circularly polarizedlight to selectively pass therethrough and which blocks a left-handedcircularly polarized light and a linearly polarized light, is disposedabove the discrimination medium 310 (first substrate 301) in thecondition shown in FIG. 4A, the condition shown in FIG. 4B is observed.In this case, by the function of the optical filter, only theright-handed circularly polarized light enters to the discriminationmedium 310, a green component of the right-handed circularly polarizedlight entering thereto is reflected by the cholesteric liquid crystallayer 302, and another wavelength component of the right-handedcircularly polarized light passes through the cholesteric liquid crystallayer 302. In this case, since the reflection light from the cholestericliquid crystal layer 302 is mainly visually observed, the hologramdisplay of characters “ABCDEFG . . . ” becomes visible in the backgroundhaving a green color at overall portions thereof. This appearance of thediscrimination medium 310 is also obtained in a case in which theoptical filter is disposed apart from the discrimination medium 310.

Next, when an optical filter, which allows a left-handed circularlypolarized light to selectively pass therethrough and which blocks aright-handed circularly polarized light and a linearly polarized light,is disposed above the discrimination medium 310 (first substrate 301) inthe condition shown in FIG. 4A, the condition shown in FIG. 4C isobserved. In this case, by the function of the optical filter, only theleft-handed circularly polarized light enters to the discriminationmedium 310, the overall components of the right-handed circularlypolarized light entering thereto pass through the cholesteric liquidcrystal layer 302, and they are not reflected by the cholesteric liquidcrystal layer 302. Thus, there is no reflection light from thecholesteric liquid crystal layer 302 (or the reflection light from thecholesteric liquid crystal layer 302 is very weak). The incident lightarrives at the print layer 305, and the pattern of the print layer 305can be preferentially observed. Thus, as shown in FIG. 4C, the blackdisplays of the patterns “▴” and “●” can be observed in the whitishbackground which is caused by the surface of the article having thediscrimination medium 310 affixed thereto. In this case, since there isno reflection light from the cholesteric liquid crystal layer 302 (orthe reflection light from the cholesteric liquid crystal layer 302 isvery weak), the displays of the patterns “▴” and “●” become more clearlyblack. This appearance is also obtained in a case in which the opticalfilter is disposed apart from the discrimination medium 310. Therefore,the authenticity of the discrimination medium 310 can be determined byusing the difference between the appearances shown in FIGS. 4A to 4C.

Example 2 of Discrimination Function of Embodiment

FIGS. 5A to 5C are conceptual diagrams showing an outline of adiscrimination function of the discrimination medium 310 shown in FIG.3E. An example will be explained in which the discrimination medium 310which is the same as in the example shown in FIGS. 4A to 4C is observedby using a discrimination viewer. FIG. 5A shows a condition in which thediscrimination medium 310 is observed from a side of the first substrate301 by a direct visual check. In this case, the same condition shown inFIG. 4A is observed.

FIG. 5B shows a discrimination viewer 321. The discrimination viewer 321is structured such that two rectangle opening portions 322 and 323 areformed at a plastic plate which blocks a visible light. The openingportion 322 of the discrimination viewer 321 has an optical filter. Thisoptical filter fitted into the opening portion 322 allows a right-handedcircularly polarized light to selectively pass therethrough and blocks aleft-handed circularly polarized light and a linearly polarized light.The opening portion 323 of the discrimination viewer 321 has an opticalfilter. This optical filter fitted into the opening portion 323 allows aleft-handed circularly polarized light to selectively pass therethroughand blocks a right-handed circularly polarized light and a linearlypolarized light.

FIG. 5C shows a condition in which the discrimination viewer 321 isdisposed above the first substrate 301 of the discrimination medium 310(with reference to FIGS. 3A to 3E), and the discrimination medium 310 isobserved via the discrimination viewer 321. In this case, since only theright-handed circularly polarized light passes through the openingportion 322, the hologram display (display of the characters “ABCDEFG .. . ”) formed on the cholesteric liquid crystal layer 302 can be moreclearly observed. On the other hand, since the right-handed circularlypolarized light is blocked at the opening portion 323 and only theleft-handed circularly polarized light passes through the openingportion 323, the hologram display (display of the characters “ABCDEFG .. . ”) formed on the cholesteric liquid crystal layer 302 cannot beobserved, and the patterns “▴” and “●” can be observed more clearlyblack. Therefore, the authenticity of the discrimination medium 310 canbe determined by using the difference between the appearances obtainedvia the opening portions 322 and 323.

Preferableness of Embodiment

The pattern of the print layer 305 is added to the hologram display ofthe cholesteric liquid crystal layer, and complicated appearances of thediscrimination medium can be thereby obtained, so that it is moredifficult to counterfeit the discrimination medium. The displays fordiscrimination are obtained by combination of the hologram displayformed on the cholesteric liquid crystal layer 302 and the figure of theprint layer 305, so that the discrimination medium can have muchinformation.

In the displays of the discrimination medium 310 shown in FIGS. 3E to5C, since an expensive block may be used in order to realize thehologram display (display of the characters “ABCDEFG . . . ” in theexamples shown in FIGS. 4A to 4C and 5A to 5C) formed on the cholestericliquid crystal layer 302, the modification of the display content mayrequire a high cost. On the other hand, since the print layer 305 isformed by a typical print method, the cost for the modification may berelatively very low. That is, in the first embodiment, the modificationof the pattern of the print layer 305 in the second substrate sidemember 32 can be performed at low cost. Therefore, the modification ofdisplays of the patterns “▴” and“●” shown in FIGS. 4A to 4C and 5A to 5Ccan be performed at low cost. As a result, the discrimination medium canbe redesigned at low cost. This effect is advantageous to manufacturingmethods for a wide variety of products in small quantities.

When the discrimination medium 310, which is directly viewed, is tilted,the discrimination medium 310 exhibits the color shift phenomenon, sothat an authenticity determination function using the color shiftphenomenon can be obtained.

2. Second Embodiment

In the first embodiment, the print layer 305 is directly formed on thecholesteric liquid crystal layer 302, and the transparent secondsubstrate 304 can be omitted. This example will be explainedhereinafter. FIGS. 6A to 6E are cross sectional views showing anotherexample of production processes for discrimination medium using thesecond embodiment of the present invention. In FIGS. 6A to 6E,explanation of portions denoted by the same reference numerals as thosein FIGS. 3A to 3E is the same as the explanation using FIGS. 3A to 3E.

First, a cholesteric liquid crystal layer 302 is formed on a transparentfirst substrate 301 (in FIG. 6A). Next, a fine asperity 303 for hologramdisplay is formed on the cholesteric liquid crystal layer 302 by using ablock for forming a hologram (in FIG. 6B). Next, printing using a blackink is performed on the surface of the cholesteric liquid crystal layer302, so that a print layer 305 having a predetermined pattern is formed(in FIG. 6C). Next, a transparent adhesive layer 306 covers the printlayer 305 so as to be formed on the cholesteric liquid crystal layer302. A release sheet 307 is affixed on the exposed surface of theadhesive layer 306. Thus, the discrimination medium 330 shown in FIG. 6Dis obtained.

When the discrimination medium 330 is affixed on an article, as shown inFIG. 6E, the release sheet 307 is peeled, and the adhesive layer 306 iscontacted on an article 331. The discrimination medium 330 can besecured on an article 331 by a function of the adhesive layer 306.

In this example, the discrimination medium 330 can be more thinned.Since setting of print conditions and the like is finer, a third personhaving no knowledge of detail production conditions cannot reproduce thediscrimination medium 330, and counterfeiting of the discriminationmedium 330 is more difficult. Since the production method for thediscrimination medium 330 is more simplified than that for the caseshown in FIGS. 3A to 3E, the production cost can be further reduced.

3. Third Embodiment

In the first embodiment and the second embodiment, the color of theprint layer 305 is not limited to black which absorbing a visible light,and the color of the print layer 305 may be another color (red, blue, orthe like) which selectively reflects light of predetermined wavelength.In this case, the display content for discrimination can be widelyproduced by combination of the print layer 305 and the cholestericliquid crystal layer 302.

4. Another Embodiment

A gap may be formed to the discrimination medium 330 by cutting. In thiscase, when the discrimination medium 330 is peeled from the article, thediscrimination medium 330 is torn at the gap and cannot be reused. Thus,illegal use of the discrimination medium can be prevented. By using thisprinciple, an open discrimination sticker, which can indicate whether apackage is broken or not, can be obtained.

A structure, which allows interlaminar fracture of discrimination medium330 when the discrimination medium 330 is peeled from the article, canbe formed to a portion of layers of the discrimination medium 330. Forexample, the interlaminar fracture position is adjusted such that beforepeeling occurs in the adhesive layer 306 or in the bond layer 308, alayer structure of the cholesteric liquid crystal layer 302 isphysically broken and separation occurs in a layer direction thereof.This adjustment can be realized by adjustment of temperature conditionsin production of the cholesteric liquid crystal layer 302.

INDUSTRIAL APPLICABILITY

The present invention can be applied to a discrimination medium used fordetermination of authenticity.

The invention claimed is:
 1. A discrimination medium comprising: acholesteric liquid crystal layer which has a fine asperity used fordisplaying a hologram; a print layer which has a predetermined patternmade of ink and which has a portion without the ink of the patternaround the pattern, wherein the portion without the ink of the patternis transparent, the pattern reflecting or absorbing a light of apredetermined wavelength; and a transparent adhesive layer, wherein thecholesteric liquid crystal layer, the print layer, and the transparentadhesive layer, are disposed in turn from a side checked visually, theprint layer is provided on a surface of the cholesteric liquid crystallayer on which the fine asperity is formed, the cholesteric liquidcrystal layer is formed on a first substrate which is opticallytransparent, and the transparent adhesive layer is in contact with theprint layer.